Diaphragm for acoustic instruments or apparatus



May 6, 1930. c. a. LENTHALL 1,757,091

DIAPHRAGM FOR ACOUSTIC INSTRUMENTS OR APPARATUS- Filed Dec. 9, 1922 &

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Patented May 6, 1930 UNITED STATES CHABLES BER'I'RAM LENTHALL, OF SOUTHPOBT. ENGLAND DIAPER-AGE FOR ACOUSTIC INSTRUMENTS OB APPARATUS Application filed. December 8, 1922, Serial No.

This invention has reference to diephragms for acoustic instruments or apparatus. The invention is more particularly applicable to the diaphragms of instruments 3. or apparatus for the reproduction of sounds, such as e. g. the sound boxes of gramophones and phonographs, telephone receivers and the like, but it is also applicable to the diaphragms of instruments or apparatus for transmitting and recording sounds, such as e. g. telephone transmitters, gramophone and phonograph record producers, dictating machines, telephonic apparatus for the use of persons with impaired hearing, and so forth. 15 The object of the invention is to provide improvements in the diaphragms of acoustic instruments and apparatus whereby to ensure a more brilliant and faithful reproduction or transmission or record of the sounds than is obtained with known diaphragms.

According to this invention a diaphragm for an acoustic instrument is provided with a concentric groove r dishing whereby the central area of the diaphragm is, so to s eak, given a tension or a stifiness which is ound to Igive improvedresults.

n the accompanying drawings Fig. 1 is a section of a gramophone sound-box fitted with one form of the improved diaphragm, and Figs. 2 and 3 are, respectively, a face view or plan and a section of the diaphragm removed.

Referring to the drawings, 4 is the soundbox and 5 is the diaphragm which is mounted therein and clamped between two packing rings 6 as usual. 7 is the stylus bar pivotally mounted on the box 4 at 8 and connected with the centre of the diaphragm at 9.

The diaphragm 5 is formed with a substantially wide and substantially shallow circumferential groove or dishing 10, the cross sectional arc of which is a segment of a circle, and the radial dimensions or Width, or the chord of the curvature, of which is approximately one-third of the radius of the diaphragm.

The diaphragm is mounted in the soundbox 4 with the convexity of the groove or dishing 10 to the outside, though if desired 605,818, and in Great Britain apru is, 1922.

the concavit of the groove or dishing may be to the outsi e.

In gramophone sound boxes excellent results have been obtained with an aluminium diaphragm of one and fifteen 'sixteenths inches diameter and .007 inch gauge, provided with a dishing or groove having a radius of one-quarter inch, a segmental angle of 105 and an outer diameter of one and three thirt -seconds inches, but I do not confine mysel to these dimensions as same may be varied and still yield improved results. The outer diameter of the dishing or groove should not, however, exceed about two-thirds of the diameter of the diaphragm, but the radius of the curvature of the dishing or roove may vary from approximately one-eig th to one-third of the diameter of the diaphragm and its segmental angle may vary from approximately 45" to 160, the largest seg 79 mental an le being used with the smallest radius an vice versa. Alternatively, the width of the dishing or groove, or the chord of the curvature thereof, may vary between about one quarter and two-thirds of the radius of the diaphragm.

The diaphragm may be made of other suitable materials than aluminium.

What I claim as my invention and desire to secure by Letters Patent is 1. For acoustic instruments or apparatus, a vibratory diaphragm provided with a single substantially wide and substantially concentric annular groove the cross sectional are of which is a segment of a circle, and the radial chord of the curvature, of which is approximately one-third of the radius of the diaphragm.

2. For acoustic instruments or apparatus, a vibratory diaphragm provided with a con- .96 centric annular groove, the diameter of the outer edge of which does not exceed twothirds of the diameter of the diaphragm, the cross sectional are of which is a segment of 160 to 45 of a circle havin a radius of from one-eighth to one-third o the diameter of the diaphragm.

3. For acoustic instruments or apparatus, a vibratory diaphragm provided with a con centric annular groove the diameter of the an outer edge of which does nct exceed twothirds of the diameter 0f the diaphragm, the cross sectional arc of which is the segment of a circle, and the chord of the curvature, of which is from one-quarter t0 twmthii'ds 0f the radius of the diaphragm. h I121 witness whereof I have hereunto set my an CHARLES BERTRAM LENTHALL. 

